The present invention relates to a foreign-matter inspection apparatus for detecting a foreign matter, scratch, defect, dirt, and the like existing on the surface of a inspection target such as a semiconductor wafer.
As disclosed in JP-A-2005-283190, in an apparatus for detecting a foreign matter (including scratch, defect, dirt, and the like) existing on the surface of a inspection target, a semiconductor wafer, the foreign matter is detected as follows: The surface of the semiconductor wafer is irradiated with laser light. Next, reflected light or scattered light is detected from the surface of the semiconductor wafer, thereby detecting the foreign matter existing on the surface thereof.
The laser beam, with which the surface of the semiconductor wafer is irradiated, is of a transversely-long elliptic shape. Moreover, the beam is emitted and applied thereto in a manner of being parallel to a camera. By maintaining this parallel state, i.e., by executing the beam irradiation in the same state always, it becomes possible to stabilize foreign-matter detection sensitivity of the foreign-matter inspection apparatus.
As described above, in the foreign-matter inspection apparatus, the foreign-matter detection sensitivity is stabilized by irradiating the surface of a inspection target with the laser light in the same state always.
In some cases, however, an assembly error occurs in the structure inside the foreign-matter inspection apparatus due to a reason such as time-lapse change. In this case, the beam with which the surface of the semiconductor wafer is irradiated cannot maintain the parallel state with respect to the camera. As a result, it turns out that the beam is emitted and applied to the semiconductor wafer in a state where the beam becomes oblique to the camera or the beam is not focused. When the beam cannot maintain the parallel state or the like with respect to the camera, the foreign-matter detection accuracy is dropped, and thus the sensitivity becomes lowered.
In the conventional technology, no consideration has been given to this point. Accordingly, there has existed a possibility that the foreign-matter detection sensitivity becomes unstable.